seams that a cage like the one in the link might be just to large for your ball, what I do ( also keep house temp in the upper 60), i have a room just for my snakes with a gas heater, or an electric one with a thermostat that keeps the room at 80, last year these was my sons room before he went to collage so we had two heating areas in the cage one at 88 one at 80 and it kept the temp well all winter long, hope it helps.